MX2015002912A - Method for separating acid gases from an aqueous flow of fluid. - Google Patents

Abstract

A method for separating acid gases from an aqueous flow of fluid is described, according to which method a) the aqueous flow of fluid is brought into contact in an absorption area with an absorbent which contains at least one amine, wherein a deacidified flow of fluid and an absorbent charged with acid gases are obtained; b) the deacidified flow of fluid is brought into contact in a washing area with an aqueous washing fluid in order to transfer, at least partially, carried amine into the washing fluid, wherein a deaminated, deacidified flow of fluid and an amine-charged washing fluid are obtained; c) the deaminated, deacidified flow of fluid is cooled downstream of the washing area, wherein an absorber top condensate is condensed out of the deaminated, deacidified flow of fluid; d) the charged absorbent is guided into a desorption area in which the acid gases are at least partially released, wherein a regenerated absorbent and desorbed acid gases are obtained; e) the regenerated absorbents are guided back into the absorption area in order to form an absorbent cycle; f) the amine-charged washing fluid and the absorber top condensate are introduced into the absorbent cycle; and g) the desorbed acid gases are guided through a reinforcement area and the acid gases coming out of the top of the reinforcement area are cooled, in order to condense a desorber top condensate out of the acid gases, which desorber top condensate is partially guided back into the reinforcement area and is partially guided out of the method. The method allows an efficient retention of amines from the treated flows of fluid while maintaining the water balance of the acid gas removal installation.

Description

PROCESS FOR THE SEPARATION OF ACID GASES FROM A FLUID CURRENT COMPRISING WATER Description The present invention relates to a process for separating acid gases from a fluid stream comprising water.

Numerous fluid streams comprise acid gases such as CO2, H2S, S02, CS2, HCN, COS or mercaptans, for example. These fluid streams can be, for example, gaseous streams such as natural gas, refinery gas, synthesis gas, combustion gases or reaction gases formed in the composting of waste materials comprising organic substances. The removal of acid gases from these fluid streams is desirable for several reasons.

The removal of carbon dioxide from flue gases serves, in particular, to reduce the emission of carbon dioxide, considered as the main cause of what is called the greenhouse effect.

The synthesis gas comprises substantially carbon monoxide and hydrogen. The synthesis gas is produced in general by partial oxidation or reforming of hydrocarbon vapor. The crude synthesis gas comprises acid gases such as carbon dioxide, hydrogen sulfide or carbonyl sulfide, which must be removed.

The content of acid gases in natural gas is reduced by appropriate treatment measures directly in the natural gas well, since they form corrosive acids in the water frequently dragged by natural gas.

On an industrial scale, to remove acid gases such as carbon dioxide, from fluid streams, aqueous solutions of organic bases are often used as absorbers, for example, amines such as, in particular, alkanolamines. When diluting acid gases, in this process, ionic products are formed from the base and acid gas components. The absorbent can be regenerated by heating, expanding to a lower pressure or distillation, where the ionic products react again to form acid gases and / or the acid gases are distilled by steam. After the regeneration process, the absorbent can be reused.

However, the amines used have a non-negligible vapor pressure. Accordingly, the fluid stream released from acid gases comprises traces of amines. Contamination of the treated fluid stream is undesirable for several reasons. For example, it is disadvantageous when, together with the treated combustion gas, traces of amines escape into the environment. The synthesis gas is the starting material for further catalytic reactions. The amine traces in this case can act as a catalyst poison. The content of amines in natural gas or liquefied petroleum gas (LPG) produced from them by liquefaction may also be subject to restrictions.

In the prior art, it has been proposed to wash the treated fluid stream with an aqueous liquid, to transfer the amine entrained at least in part to the aqueous liquid.

EP 0 798 029 A2 discloses a process in which a gas is treated with a basic amine compound for the absorption of carbon dioxide and the treated gas is then put in contact with an aqueous phase of 20 to 60 ° C, in order to transfer basic amine entrained at least in part to the aqueous phase. It is said that the aqueous phase is preferably a condensate that condenses from the carbon dioxide released in the regeneration tower.

EP 0 502 596 A1 teaches a process for removing CO2 from a combustion exhaust gas, wherein the combustion exhaust gas is contacted, in a first section, with an absorbent comprising an aqueous solution of an alkanolamine , water is condensed from the combustion exhaust gas by cooling and the condensing water is contacted in a second section with the combustion exhaust gas that is depleted in carbon dioxide.

EP 1 132 125 A1 discloses a process for controlling the concentration of an absorbent in a system for separating C02, wherein the temperature of the circulating water in a washing zone is controlled as a function of the liquid level in the lower part of the absorption tower.

EP 1 334 759 A1 teaches a process and a device for recovering amine, wherein the amine which is present in a gaseous stream released from C02 is removed from the gas stream by a plurality of successive washing steps.

US 2008/0159937 comprises a process for removing carbon dioxide from a gaseous stream, wherein the gaseous stream that is depleted in carbon dioxide is washed with water in a packing section of the absorption column. The water can be condensed from the top of the regeneration column or fresh water to compensate for the loss of the quantities.

An acid gas removal system loses water continuously in the form of steam, which is removed by means of the treated fluid stream and acid gases that are released or due to other physical losses. In order to compensate the losses and maintain the water balance of the system, it is therefore necessary, in general, to add fresh water periodically to the absorbent circuit to compensate for quantity losses (constitution of water). Fresh water to compensate for the loss of quantities should not include dissolved substances and, for example, is demineralized water or steam condensate.

On the other hand, under certain conditions, more water can be introduced into the acid gas removal system that is removed by means of the treated fluid stream and the acid gases released. This is the case, in particular, if (i) the fluid stream that has to be treated has a high water content or is saturated with water vapor, (i) the treated fluid stream cools a lot in the area of washing or downstream of the washing zone in order to ensure an effective amine retention, and / or (iii) the fluid stream to be treated has a relatively low acid gas content and the flow rate volumetric of the acid gases released in the regenerator is, therefore, small.

In these cases, it is necessary to remove the water from the acid gas removal system in order to avoid uncontrolled dilution of the absorbent by condensed water inside.

EP 2 228 1 19 A1 teaches a process for removing acid gases from a gas where a part of the water present in the acid gases obtained is removed. This can be achieved because a part of the upper condenser of the regenerator is removed and does not pass as reflux to the regenerator.

The condensate streams of an acid gas removal system comprise greater or lesser amounts of amines. When a sub-quantity of a condensate stream is discharged, small quantities of amines are consequently removed from the system in a continuous manner. This causes economic and ecological problems. First, wastewater, for safe disposal, must be treated in a complex manner. Secondly, amine losses must be replaced continuously or periodically. Although it would be possible to recover amines present from the condensate discharged, for example, by distillation, these methods, due to their high energy demand, are generally not economically viable.

The object of the present invention is to specify a process for removing acid gases from fluid streams comprising water, in particular to remove acid gases from natural gas, which substantially allows without additional energy demand an effective retention of amines from the treated fluid streams, safeguarding the water balance of the acid gas removal system.

The object is achieved by means of a process for separating acid gases from a fluid stream comprising water, wherein a) the fluid stream comprising water is contacted in an absorption zone with an absorbent comprising at least an amine, where a stream of deacidified fluid and an absorbent loaded with acid gas is obtained, b) the deacidified fluid stream is brought into contact in a washing zone with an aqueous washing liquid, in order to transfer amine entrained at least in part to the washing liquid, where a deacidified, deaminated fluid stream is obtained and a washing liquid loaded with amine, c) the deacidified, deaminated fluid stream is cooled downstream of the wash zone, where an upper absorbent condensate is condensed from the deamidated, deacidified fluid stream, d) the charged absorbent is passed to a desorption zone where the acid gases are released at least in part, where a regenerated absorbent and desorbed acid gases are obtained, e) the regenerated absorbent returns to the absorption zone in order to form an absorbent circuit, f) the washing liquid loaded with amine and the upper absorbent condensate are introduced into the absorbent circuit, and g) the desorbed acid gases are conducted through an enrichment zone and the acid gases that exit at the top of the enrichment zone are cooled, in order to condense a desorbent condensate from the acid gases that partly returns to the zone of enrichment and partly leaves the process. The fluid stream comprising water is contacted with an absorbent comprising at least one amine in an absorption zone. In this process, an at least partially deacidified fluid stream is obtained (in the present case, called deacidified fluid stream) and an absorbent charged with acid gases. The treatment of the fluid stream with the absorber proceeds preferably in countercurrent. The fluid stream in this case is generally fed in a lower region and the absorber in a higher region of the absorption zone. To improve the contact and provide a large surface area of mass transfer, the absorption zone generally comprises internal parts, for example, packed beds, packings and / or trays. The fluid stream is treated with the absorbent in an appropriate manner in an absorption tower or an absorption column, for example, a randomly packed column, a structured packing column or a column of trays. The absorption zone is considered to be a section of an absorption column in which the fluid stream comes into mass transfer contact with the absorbent.

The temperature of the absorbent introduced into the absorption zone it is generally about 20 to 60 ° C.

The deacidified fluid stream is then brought into contact in a washing zone with an aqueous washing liquid, in order to transfer amine entrained at least in part in a washing liquid. In this process, a deacidified, deaminated fluid stream and a washing liquid loaded with amine are obtained. The washing according to the invention of the deacidified fluid stream using the aqueous washing liquid allows the removal of most of the entrained amine and also optionally of entrained amine decomposition products.

As the aqueous washing liquid, aqueous liquids are widely available which are largely free of amines and amine decomposition products. Typically, the washing liquid comprises less than 2% by weight, preferably less than 1% by weight, with particular preference, less than 5000 ppm by weight of amines and amine decomposition products. The washing liquid may be intrinsic liquids, i.e., aqueous liquids arising at another process site or aqueous liquids provided externally.

Preferably, the washing liquid comprises upper sorbent condensate, desorbent upper condensate and / or fresh water.

In preferred embodiments, the wash liquid is formed wholly or partly by upper sorbent condensate which is produced in the cooling downstream of the deacidified, deaminated fluid stream and passed into the wash zone. In order to achieve a sufficient wetting of the internal parts in the area of washing, it may be desirable, in addition to passing more aqueous liquid to the washing area. In a preferred embodiment, consequently, a little of the desorbent upper condensate is passed as a washing liquid to the washing zone. The use of the higher desorbent condensate as an additional aqueous liquid is preferred because it has no effect on the water balance of the general system and this aqueous phase is largely free of amine impurities. In certain embodiments, the washing liquid also comprises fresh water (constitution of water), which is passed to the washing area.

In certain cases, it may be preferred that the washing liquid does not comprise a superior absorbent condensate and is formed, for example, exclusively of desorbent upper condensate and / or fresh water. This is the case, for example, when the upper absorbent condensate comprises volatile hydrophobic components, such as hydrocarbons, which, together with the aqueous condensate, are condensed from the deamidated, deacidified fluid stream. The upper biphasic absorbent condensate can lead, in these cases, to an undesirable formation of foam in the washing zone. In these cases, it may be advantageous to combine the upper absorbent condensate with the charged absorbent, for example, by passing the upper absorbent condensate to an expansion vessel described hereinbelow.

In the washing zone, the washing liquid is conducted in countercurrent against the deacidified fluid stream. Preferably, the wash zone comprises random packings, Structured packings and / or trays, in order to intensify the contact between the fluid stream and the washing liquid. The washing liquid can be distributed in the cross section of the washing area by means of distributors of suitable liquids on the washing area.

In preferred embodiments, the wash zone is constructed as a section of an absorption column disposed over the absorption zone. The washing zone for this purpose is a section constructed as a backwash section or enrichment part of the absorption column on the adsorbent feed.

In one embodiment, the wash liquid is recolored through the wash zone. The washing liquid is collected for this purpose below the washing zone, for example, by an appropriate collecting tray and is pumped by means of a pump to the upper end of the washing zone. The recycled washing liquid can be cooled, preferably to a temperature of 20 to 70 ° C, in particular 30 to 60 ° C. For this purpose, the washing liquid is suitably pumped in circulation by means of a refrigerator. In order to avoid an accumulation of washing absorbent components in the washing liquid, a substream of washing liquid from the washing zone passes as washing liquid loaded with amine. By optional recycling and cooling of the washing liquid, the washing action can be increased. However, in recycling, backmixing of the washing liquid occurs. At high recycling ratios, in the washing area, only a maximum effect of a theoretical separation step can be achieved, regardless of the length of the contact section in the wash zone. The reclining ratio is defined as the ratio of the amount of the wash liquid pumped in circulation to the amount of past substream. When the washing liquid is recycled, consequently, only a limited reduction in the concentration of amines entrained in the deacidified fluid stream can be achieved. Therefore, the recycling of the washing liquid is not preferred.

In a preferred embodiment, the aqueous washing liquid is conducted in a single passage through the washing zone without pumping it in circulation. The washing liquid flowing out of the washing zone is preferably passed to the absorption zone.

After leaving the wash zone, the deacidified, deaminated fluid stream is saturated with water vapor. With the water vapor, the deacidified, deamidated fluid stream still drags traces of amines and / or amine decomposition products. For a subsequent removal of the entrained amines and / or amine decomposition products, the deacidified, deaminated fluid stream is cooled downstream (based on the flow direction of the deamidated, deacidified fluid stream) of the wash zone , where an aqueous condensate condenses. The aqueous condensate is referred to in the present case as an absorbent top condensate.

The deacidified, deaminated fluid stream is preferably cooled to a temperature of 5 ° C to 40 ° C, preferably particular, up to a temperature of 17 ° C to 27 ° C. Conveniently, the deacidified, deaminated fluid stream is cooled to a temperature that is lower than the temperature of the fluid stream comprising water. The temperature difference between the deacidified, deamidated fluid stream cooled and the fluid stream comprising water is, for example, at least 2 K, preferably at least 5 K, particularly preferably at least 10 K , most preferably, from 10 to 30 K. With a greater temperature difference, a larger fraction of water present in the deacidified fluid stream comprising water is condensed as higher absorbent condensate together with residual amounts of amine dissolved therein.

The cooling of the deacidified, deaminated fluid stream downstream of the washing zone proceeds, preferably, by indirect heat exchange (indirect cooling). As an indirect cooler, all heat exchangers that are suitable for cooling gases or fluids are suitable. Suitable heat exchangers are, for example, sheath and tube heat exchangers. The deacidified, deaminated fluid stream flows down through the tubes of the heat exchanger. The cooling medium flows upwards through the heat exchanger sheath. During the cooling of the deamidated, deacidified fluid stream, the liquid condenses in the tubes and flows downwards. To separate the upper absorbent condensate, use a phase separation unit or a separator (drum knock-out) Although the upper absorbent condensate comprises only small amounts of dissolved amines and / or amine decomposition products, it can be passed as washing liquid to the washing zone.

In order to avoid a loss of the amines present in the amine-laden washing liquid and in the upper absorbent condensate, the amine-laden washing liquid and the upper absorbent condensate are introduced into the absorbent circuit. This can proceed by direct or indirect combination with the charged and / or regenerated absorber.

The direct combination with the adsorbent refers to the direct introduction of the washing liquid loaded with amine and / or of the upper absorbent condensate into the charged and / or regenerated absorbent, for example, in a conduit that conducts the absorbent or regenerated in the bottom of the absorption column or desorption column. The indirect combination with the absorbent refers to the amine-laden washing liquid and / or the superior absorbent condensate is first used, for example, for washing or cooling of fluid streams, but is finally combined with the charged absorbent and / or regenerated.

In general, it is preferred to pass the washing liquid loaded with amine to the absorption zone where the washing liquid loaded with amine is combined with the absorbent. The upper absorbent condensate is preferably passed as washing liquid to the washing zone.

The absorbent charged with acid gases is passed to a desorption zone where the acid gases are released at least in part. In In this process, a regenerated absorbent is obtained that returns to the absorption zone and desorbed acid gases.

In general, the charged absorption liquid is regenerated by heating, for example, from 70 to 150 ° C, expansion, distillation with an inert fluid or a combination of two or all of these measures. Preferably, the charged absorption liquid is regenerated in a distiller. The distillation gas required for the distillation is generated by partial evaporation of the absorption liquid in the lower part of the distiller.

The preferred configuration of desorption depends on the pressure in the absorption zone. If the fluid stream comprising water has a greatly increased pressure compared to the surrounding atmosphere of 20 to 120 bar, preferably, from 35 to 95 bar, with particular preference, from 50 to 70 bar, for desorption, the expansion is suggested up to a pressure of 0.5 to 5 bar, preferably, from 0.7 to 3.5. bar, with particular preference, from 0.9 to 2.0 bar. If the fluid stream comprising water has a pressure of 0.5 to 5 bar, preferably 0.7 to 3.5 bar, particularly preferably 0.9 to 2.0 bar, for desorption, it is suggested to heat the absorbent charged with acid gases to a temperature of 20 to 150 ° C, preferably 100 to 140 ° C, particularly preferably 110 to 130 ° C. In a preferred embodiment, for the regeneration of the absorbent charged with acid gases, it expands and is heated in the desorption zone.

In a preferred embodiment, the charged absorbent is It expands in an expansion vessel, where a gaseous phase and an expanded absorbent are obtained. The expanded absorbent is then passed to the desorption zone. In the expansion, coabsorbed components are released from the fluid stream such as inert gases, oxygen and / or hydrocarbons. In the expansion, a small part of the acid gases can also be released. In the expansion vessel, the pressure is preferably set such that the majority of acid gases are not released. In certain embodiments, the pressure in the expansion vessel may be from 1.0 to 9 bar, preferably from 1.5 to 6 bar. The pressure may be only slightly higher or even lower than the pressure in the desorption zone, which is why the expanded absorbent is pumped in certain embodiments from the expansion vessel to the desorption zone.

In certain embodiments, the upper absorbent condensate is passed partially or fully into the expansion vessel and, thus, is introduced into the absorbent circuit. This is preferred when the upper absorbent condensate comprises volatile hydrophobic components such as hydrocarbons. In the expansion vessel, the volatile components of the upper absorbent condensate can escape together with the gas phase.

Before introducing the regenerated absorbent back into the absorption zone, it is cooled down to an appropriate absorption temperature. In order to utilize the energy present in the hot regenerated absorbent, it is preferred to preheat the charged absorbent from the absorption by indirect heat exchange with the hot regenerated absorbent. By means of the heat exchanger, the charged absorbent is brought to a higher temperature in such a way that, in the regeneration stage, a lower energy input is required. In addition, a partial regeneration of the charged absorbent with the release of acid gases can be carried out by means of heat exchange.

The desorbed acid gases are conducted according to the invention through an enrichment zone. The acid gases that exit at the top of the enrichment zone are cooled in order to condense an aqueous phase which is referred to herein as a higher desorbent condensate. The desorbent upper condensate partly returns as reflux to the enrichment zone and partly leaves the process. By passing a part of the desorbent upper condensate, the water balance of the general system is maintained and an accumulation of water in the system is avoided. The passage can be carried out, for example, using a controllable reflux divider. A part of the desorbent upper condensate is passed, preferably, according to maintenance of the water balance in the process. Parameters such as the liquid level in certain containers of the absorbent circuit or the concentration of the amine in the absorbent can be measured continuously or periodically and can be used to control the amount of the higher desorbent condensate that was passed. An appropriate range of the absorber circuit for the measurement of the liquid level is distinguished because the filling level rises when the it accumulates water in the absorbent circuit and falls when water is lost. Preferably, the measurement of the liquid level proceeds at the bottom of the desorption column or in a buffer vessel communicating with the absorbent circuit.

The enrichment zone through which the desorbed acid gases are passed is preferably disposed on the desorption zone and, in a particularly preferred embodiment, is disposed on the desorption zone and integrated into the column of desorption.

The enrichment zone suitably has a structured packing, a random packing and / or a plurality of trays. Preferably, the structured packing or the random packing has a height of at least 1.5 meters, in particular at least 1, 8 meters. The height of structured packing or random packing is, for example, up to 3.0 meters. The geometric surface area of the structured packing of the enrichment zone can be between 100 and 600 m2 / m3, preferably between 140 and 500 m2 / m3, with particular preference, between 180 and 400 m2 / m3.

If the enrichment zone comprises trays, the number of trays is preferably at least 4, in particular at least 5, more preferably at least 6 and most preferably at least 8. The amount of trays can be up to 14, preferably up to 12 or up to 10. A tray count of 6 to 10 is generally preferred.

In the enrichment zone, the traces of the amines entrained by the released acid gases are expelled when a part of the desorbent upper condensate is returned, in such a way that the acid gases that exit at the top of the enrichment zone are largely released. of the amine impurities. The condensing upper desorbent condensate of the acid gases leaving the top of the enrichment zone is likewise largely free of amine impurities and part of the process can be passed without a significant loss of amine. The greater the separation efficiency of the enrichment zone, the lower the losses of amines by means of the acid gas stream.

The upper desorbent condensate comprises less than 500 ppm by weight, preferably less than 300 ppm by weight, more preferably less than 200 ppm by weight, with particular preference, less than 100 ppm by weight, with very particular preference, less of 50 ppm by weight, most preferably less than 30 ppm by weight of amines and amine decomposition products.

The process according to the invention is suitable for treating fluid streams comprising water, in particular gas streams comprising water of all types. Acid gases are, in particular, CO2, H2S, COS and mercaptans. In addition, S03, S02, CS2 and HCN can also be removed. In general, the acid gases comprise at least C02 or predominantly comprise C02.

In a preferred embodiment, the fluid stream comprising water has a water content of at least 20%, with preference, of at least 30%, with particular preference, of at least 40% of the water saturation concentration. The saturation concentration refers to the concentration of water or water vapor in the fluid stream under the conditions of temperature and pressure at which the fluid stream is introduced into the absorption zone, in excess of which the water forms a Separate phase in the fluid stream due to falling below the dew point.

In a preferred embodiment, the fluid stream comprising water is conducted in the absorption zone at a pressure of from 20 to 120 bar, preferably from 35 to 95 bar, particularly preferably from 50 to 70 bar.

All pressures cited in this document are absolute pressures.

In an alternative preferred embodiment, the fluid stream comprising water is conducted to the absorption zone at a pressure of 0.1 to 10 bar, preferably 0.3 to 3 bar, particularly preferably 0 , 6 to 1, 5 bar.

In a preferred embodiment, the fluid stream comprising water has a partial pressure of acid gas that is 2.5 bar or less, preferably 1 bar or less, particularly preferably 500 mbar or less.

The fluid streams comprising water comprising the acid gases are first of all gases such as natural gas, synthesis gas, coke oven gas, cracked gas, coal gasification gas, circulation gas, landfill gases and exhaust gases. combustion and secondly, liquids that are substantially immiscible with the absorber, such as liquefied petroleum gas (LPG) or natural gas liquids (NGL).

In preferred embodiments, the fluid stream comprising water is a (i) fluid stream comprising hydrogen; they include synthesis gases that can be produced, for example, by coal gasification or steam reforming and optionally subjected to an aqueous gas stream reaction; the synthesis gases are used, for example, to produce ammonia, methanol, formaldehyde, acetic acid, urea, for the Fischer-Tropsch synthesis or for the recovery of energy in an integrated cycle process combined with gasification (IGCC); (ii) fluid stream comprising hydrocarbons; include natural gas, exhaust gases from various refinery processes, such as from the waste gas unit (TGU), from a visco-reducer (VDU), from a catalytic cracker (LRCUU / FCC), from a hydrocracker (HCU), from a hydrotreater (HDS / HTU), a coker (DCU), an atmospheric distillation (CDU) or a liquid treater (for example, LPG).

The process according to the invention is suitable for treating fluid streams comprising oxygen, such as combustion gases.

In preferred embodiments, the fluid stream comprising oxygen originates from a) the oxidation of organic substances, b) composting or storage of waste materials that comprise organic substances, or c) bacterial decomposition of organic substances.

In some embodiments, the partial pressure of carbon dioxide in the fluid stream is less than 500 mbar, for example, 30 to 150 mbar.

The oxidation can be carried out as a flame, that is, as conventional combustion or as an oxidation without a flame appearance, for example, in the form of catalytic oxidation or partial oxidation. The organic substances that are subjected to combustion are usually fossil fuels such as coal, natural gas, petroleum, gasoline, diesel, refined or kerosene, biodiesel or waste materials that have a content of organic substances. The starting materials of (partial) catalytic oxidation are, for example, methanol or methane, which can be converted to formic acid or formaldehyde.

Waste materials that are subjected to oxidation, composting or storage are typically household waste, plastic waste or packaging waste.

The combustion of organic substances proceeds mostly in usual combustion plants with air. The composting and storage of waste materials that comprise organic substances in general proceeds in landfills. The exhaust gas or the exhaust air of such systems can be advantageously treated by means of of the process according to the invention.

The organic substances that are used for bacterial decomposition are usually stable manure, straw, liquid manure, sewage sludge, fermentation residues, silage and the like. Bacterial decomposition comes, for example, in usual biogas plants. The exhaust air of such plants can be advantageously treated by the process according to the invention.

The process is also suitable for treating exhaust gases from fuel cells or chemical synthesis plants that make use of (partial) oxidation of organic substances.

The absorbent comprises at least one amine. Preferably, the amine comprises at least one primary or secondary amine.

The preferred amines are the following: (i) amines of the formula I: NR1 (R2) 2 (I) where R1 is selected from C2-C6 hydroxyalkyl groups, C1-C6 alkoxy-C2-C6 alkyl groups, C6-C6-C6-C6-C6-C2-C6-C6 alkoxy groups and C2-C6-piperazinyl-C2-C6 alkyl groups and R2 is selected, independently, of H, C-C6 alkyl groups and C2-C6 hydroxyalkyl groups; (ii) amines of formula II: R3R4N-X-NR5R6 (II) where R3, R4, R5 and R6 are independently selected from Ci-C6 alkyl groups, C2-C3 hydroxyalkyl groups, Ci-C6 alkoxy groups, C2-C6 alkyl and C2-C6 aminoalkyl groups and X is a alkylene group C2-C6, -X1-NR7-X2- O -X1-O-X2-, where X1 and X2 are, so independent of each other, C2-C6 alkylene groups and R7 is H, a CrC6 alkyl group, a C2-C6 hydroxyalkyl group or a C2-C6 aminoalkyl group; (iii) saturated 5- to 7-membered heterocycles having at least one nitrogen atom in the ring, which may comprise one or two more heteroatoms selected from nitrogen and oxygen in the ring and (iv) mixtures of them.

Specific examples are: (i) 2-aminoethanol (monoethanolamine), 2- (methylamino) ethanol, 2- (ethylamine) ethanol, 2- (n-butylamino) ethanol, 2-amino-2-methylpropanol, N- (2-aminoethylpiperazine, methyldiethanolamine, ethyldiethanolamine, dimethylamidopropanol, t-butylaminoethoxyethanol, 2-aminomethylpropanol; (ii) 3-methylaminopropylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, 2,2-dimethyl-1,3-diaminopropane, hexamethylenediamine, 1,4-diminobutane, 3,3-iminobispropylamine, tris (2-aminoethyl) amine, bis (3) -dimethylamino-propyl) amine, tetramethylhexamethylenediamine; (iii) piperazine, 2-methylpiperazine, N-methylpiperazine, 1-hydroxyethylpiperazine, 1,4-bishydroxyethylpiperazine, 4-hydroxyethylpiperidine, homopiperazine, piperidine, 2-hydroxyethylpiperidine and morpholine; Y (iv) mixtures of them.

In a preferred embodiment, the absorbent comprises at least one of the amines monoethanolamine (MEA), methylaminopropylamine (MAPA), piperazine, diethanolamine (DEA), triethanolamine (TEA), diethylethanolamine (DEEA), diisopropylamine (DIPA), aminoethoxyethanol ( ESA), dimethylaminopropanol (DIMAP) and methyldiethanolamine (MDEA) or mixtures thereof.

In general, the absorbent comprises 10 to 60% by weight of amine.

The absorbent may also comprise additives, such as corrosion inhibitors, enzymes, etc. In general, the amount of such additives is in the range of about 0.01 -3% by weight of the absorbent.

The invention will be described in more detail by means of the accompanying drawings and the following examples.

Figure 1 schematically shows a plant for carrying out a process not according to the invention, wherein, for the maintenance of the water balance, a little of the aqueous condensate is passed from the deamidated, deacidified fluid stream.

Figure 2 schematically shows a plant for carrying out a process not according to the invention, wherein, for the maintenance of the water balance, a little aqueous condensate is passed from the acid gases desorbed, where the acid gases are not They drive through an enrichment zone.

Figure 3 shows an appropriate plant for carrying out the process according to the invention. The desorbed acid gases are conducted through an enrichment zone before condensing an upper condensate desorbing the acid gases desorbed and partly passing out.

According to Figure 1, a fluid stream comprising water 1 is passed to the bottom of an absorption column 2. The absorption column 2 has an absorption zone 3 and a washing zone 4. In the absorption zone 3, the fluid stream comprising water is brought into countercurrent contact with an absorbent which is introduced into the absorption column 2 over the absorption zone through the tube 5. The deacidified fluid stream is washed in the washing zone 4 with an aqueous condensate and fresh water, where the aqueous condensate is obtained by cooling the deacidified fluid stream, deaminated in the refrigerator 6, is collected in the phase separation vessel 7 and passed through the tube 8 to the washing zone. The fresh water is carried by means of the tube 9. The treated gas stream leaves the phase separation vessel 7 via the tube 23. A part of the aqueous condensate is passed through the tube 25, where the accumulation of water is prevented in the absorbent.

The absorbent charged with acid gases is removed in the lower part of the absorption column 2 and expanded in the expansion vessel 10 through a butterfly valve (not shown). The expansion leads to the desorption of the coabsorbed components of the fluid stream and some of the acid gases that are extracted by means of the stream 24. The expanded absorbent is conducted through a heat exchanger 11 and the tube 12 in a desorption column 13. The desorption column 13 has a desorption zone 14. At the bottom of the desorption column 13, the expanded absorbent is heated by means of the evaporator 15 and partially vaporized. By raising the temperature, the acid gases absorbed The acid gases are removed in the upper part of the desorption column 13 by means of the tube 16 and are fed to the refrigerator 17. In the refrigerator 17, a desorbent upper condensate is obtained which is collected in the separation container of phases 18 and return to the desorption column. The acid gases are removed as stream 19. The regenerated absorbent 20 is returned to the absorption column 2 by means of the heat exchanger 11, the pump 21, the refrigerator 22 and the tube 5.

In figure 2, the same reference signs have the same meaning as in figure 1. Contrary to fig. 1, no aqueous condensate is passed through the phase separation vessel 7. To maintain water balance, a little of the upper desorbent condensate that appears in the phase separation vessel 18 is passed through the tube 26.

Figure 3 shows an embodiment according to the invention. In Figure 3, the same reference signs have the same meaning as in Figure 1. Compared with the process shown in Figure 2, in the upper region of the desorption column, enrichment zone 28 was integrated. maintaining the water balance, a part of the upper desorbent condensate that appears in the phase separation vessel 18 is passed through the tube 27.

Comparative example 1 Calculations were made using a simulation model. Base of the simulation model is a thermodynamic model based on the electrolyte-NRTL approach of Chen et al. (Chen, CC; Evans, LB: A local Composition Model for the Excess Gibbs Energy of Aqueous Electrolite Solutions, AIChE J. (1986) 32 (3), 444), with the use of which phase equilibrium can be described for this system. The simulation of absorption processes is described using an approach based on mass transfer; the details of it are described by Asprion (Asprion, N .: Nonequilibrium Rate-Based Simulation of Reactive Systems: Simulation Model, Heat Transfer and Influence of Film Discretization, Ind. Eng. Chem. Res. (2006) 45 (6), 2054-2069).

A process was simulated in a plant according to figure 1. The absorption column 2 had a diameter of 2220 mm and had two random packages 3 (INTALOX® Metal Tower Packing IMTP 25, Koch-Glitsch, Wichita, United States), each with a packing height of 4 meters. The washing area 4 comprised 3 trays. The desorption column 13 had a diameter of 1220 mm and had two random packings 14 (PRM 35, from Pall Corporation, Port Washington, NY, United States), each with a packing height of 5 meters.

An aqueous solution with 32% by weight of methyldiethanolamine and 8% by weight of piperazine was used as an absorbent. The absorber was passed to the absorption zone at 60262 kg / h at a temperature of 40 ° C via tube 5. As a fluid stream comprising water, 151609 kg / h of natural gas (88.52% by volume) were fed. of CH4, 9.72% by volume of C2H6, 0.94% by volume of CO2, 0.58% by volume volume of N2, 0.23% by volume of H2O) at a temperature of 35 ° C and a pressure of 53.7 bar. The feed of wash water to the washing zone 4 was 197 kg / h, where the wash water comprised 194 kg / h of cooled recirculated water condensate to 22 ° C and 3 kg / h of fresh water (constitution of Water). Of the total of 358 kg / h of aqueous condensate arising through the cooler 6 and phase separation vessel 7, 164 kg / hr was passed through the tube 25. Through the tube 23, 147205 kg / hr of natural gas The treated process was left at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 2 ppm by volume. 64505 kg / h of absorption solution charged with acid gases were extracted at a temperature of 39.8 ° C at the lower end of the absorption zone and expanded to a pressure of 6 bar in the expansion vessel 10. In the upper part of the expansion vessel 10, 639 kg / hr of desorbed gases were extracted which substantially comprised methane and ethane.

The absorbent was removed in the lower part of the expansion vessel 10 and was passed through the heat exchanger 1 1 into the desorption column 13 and heated there by means of the evapor 15 to 130.9 ° C. The desorbed acid gases were cooled from 1 13.5 ° C to 40 ° C in the refriger 17. The 2272 kg / h of aqueous phase formed in this process were separated from the acid gases in the phase separation unit 18 and They happened again in the column of desorption.

The annual loss of amine from the plant is 6,366 t; this is equivalent to 53% of the 12 t of amine originally used.

Comparative example 2 A process was simulated in a plant according to Figure 2. The structure of the absorption column 2 and the desorption column 13 corresponds to that of comparative example 1 The composition of the absorbent and the fluid stream correspond to the comparative example 1. The absorbent was passed to the absorption zone by means of the tube 5 at 60263 kg / h at a temperature of 40 ° C. 151609 kg / h of natural gas were fed at a temperature of 35 ° C and a pressure of 53.7 bar. The washing water feed in the washing zone 4 was 361 kg / h where the wash water comprised 358 kg / h of fresh recirculated water condensate cooled to 22 ° C and 3 kg / h of fresh water. Through tube 23, 147206 kg / h of treated natural gas left the process at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 3 ppm in volume. 64834 kg / h of absorption solution charged with acid gases were passed into the lower end of the absorption zone at a temperature of 39.8 ° C and expanded to a pressure of 6 bar in the expansion vessel 10. In the upper part of the expansion vessel 10, 638 kg / hr of desorbed gas desorbed gases comprising substantially methane and ethane were extracted.

The absorber was removed at the bottom of the expansion vessel 10 and was conducted through the heat exchanger 11 in the desorption column 13 and heated there by means of the evapor 15 to 130.8 ° C. The desorbed acid gases were cooled in the refriger 17 from 13.5 ° C to 40 ° C. The 2102 kg / h of aqueous phase formed in this process were separated from the acid gases in the phase separation unit 18. 165 kg / h were removed from the upper desorbent condensate and the rest was passed back into the desorption column.

The annual amine loss is 5,671 t; this is equivalent to 47% of the 12 t of the amine originally used.

Example 3 according to the invention A process according to the invention was simulated in a plant according to figure 3. The structure of the absorption column 2 and the desorption column 13 corresponds to comparative example 1, where, however, in the desorption column , on the feeding of the absorption medium charged by means of the tube 12, an enrichment zone 28 having 4 trays was installed.

The composition of the absorbent and the fluid stream corresponds to comparative example 1. The absorbent was passed to the absorption zone by means of tube 5 at 60279 kg / h at a temperature of 40 ° C. 151609 kg / h of natural gas were fed at a temperature of 35 ° C and a pressure of 53.7 bar. The feed of washing water in the washing zone 4 was 363 kg / h, where the washing water comprised 359 kg / h of fresh recirculated water condensate cooled to 22 ° C and 4 kg / h of fresh water. Through the tube 23, 147208 kg / h of gas The treated natural gas left the process at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 3 ppm by volume. 64849 kg / h of absorption solution charged with acid gases were passed at the lower end of the absorption zone at a temperature of 39.8 ° C and expanded to a pressure of 6 bar in the expansion vessel 10. In the upper part of the expansion vessel 10, 636 kg / hr of desorbed gases were extracted which substantially comprised methane and ethane.

The absorbent was removed in the lower part of the expansion vessel 10 and was passed through the heat exchanger 1 1 in the desorption column 13 and heated there by means of the evaporator 15 to 130.8 ° C. The desorbed acid gases were cooled in the refrigerator 17 from 13.4 ° C to 40 ° C. The 1875 kg / h of aqueous phase formed in this process was separated from the acid gases in the phase separation unit 18. From the higher desorbent condensate, 165 kg / h were removed and the rest was passed back into the desorption column.

The annual amine loss is 0.396 t; this is equivalent to 3.3% of the 12 t of the amine originally used.

Example 4 according to the invention Example 3 is repeated, but enrichment zone 28 had 5 trays.

The absorbent was transferred to the absorption zone at 60279 kg / h at a temperature of 40 ° C by means of tube 5. 151609 kg / h of natural gas were fed at a temperature of 35 ° C and a pressure of 53.7 bar. The washing water feed in the washing zone 4 was 364 kg / h, where the washing water comprised 359 kg / h of fresh recirculated water condensate cooled to 22 ° C and 5 kg / h of fresh water. Through tube 23, 147208 kg / h of treated natural gas left the process at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 3 ppm in volume. 64849 kg / h of absorption solution charged with acid gases were passed at the lower end of the absorption zone at a temperature of 39.8 ° C and expanded to a pressure of 6 bar in the expansion vessel 10. In the upper part of the expansion vessel 10, 636 kg / hr of desorbed gases comprising substantially methane and ethane were extracted.

The absorbent was removed in the lower part of the expansion vessel 10 and was passed through the heat exchanger 1 1 in the desorption column 13 and heated there by means of the evaporator 15 to 130.8 ° C. The desorbed acid gases were cooled from 113.4 ° C to 40 ° C in the refrigerator 17. The 1875 kg / h of aqueous phase formed in this process was separated from the acid gases in the phase separation unit 18. From the condensate upper desorbent, 165 kg / h were removed and the rest was passed again in the desorption column.

The annual amine loss is 0.231 t; this is equivalent to 1.93% of the 12 t of the amine originally used.

Example 5 according to the invention Example 3 is repeated, but enrichment zone 28 had 6 trays.

The absorbent was passed to the absorption zone by means of tube 5 at 60279 kg / h at a temperature of 40 ° C. 151609 kg / h of natural gas were fed at a temperature of 35 ° C and a pressure of 53.7 bar. The washing water feed in the washing zone 4 was 364 kg / h, where the washing water comprised 359 kg / h of fresh recirculated water condensate cooled to 22 ° C and 5 kg / h of fresh water. Through tube 23, 147208 kg / h of treated natural gas left the process at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 3 ppm in volume. 64849 kg / h of absorption solution charged with acid gases were passed at the lower end of the absorption zone at a temperature of 39.8 ° C and expanded to a pressure of 6 bar in the expansion vessel 10. In the upper part of the expansion vessel 10, 636 kg / hr of desorbed gases comprising substantially methane and ethane were extracted.

The absorbent was removed at the bottom of the expansion vessel 10 and conducted through the heat exchanger 1 1 in the desorption column 13 and heated thereto up to 130.8 ° C by the evaporator 15. The acid gases desorbed were cooled from 113.4 ° C to 40 ° C in the refrigerator 17. The 1875 kg / h of aqueous phase formed in this process was separated from the acid gases in the phase separation unit 18. From the desorbent top condensate, the they removed 165 kg / h and the rest was passed again in the desorption column.

The annual amine loss is 0, 152 t; this is equivalent to 1.27% of the 12 t of the originally used amine.

Example 6 according to the invention Example 3 is repeated, but enrichment zone 28 had 8 trays.

The absorbent was passed to the absorption zone by means of tube 5 at 60279 kg / h at a temperature of 40 ° C. 151609 kg / h of natural gas were fed at a temperature of 35 ° C and a pressure of 53.7 bar. The washing water feed in the washing zone 4 was 364 kg / h, where the washing water comprised 359 kg / h of fresh recirculated water condensate cooled to 22 ° C and 5 kg / h of fresh water. Through tube 23, 147208 kg / h of treated natural gas left the process at a temperature of 22 ° C, a pressure of 53.6 bar, a water content of 0.094% by volume and a CO2 content of 3 ppm in volume. 64849 kg / h of absorption solution charged with acid gases were passed at the lower end of the absorption zone at a temperature of 39.8 ° C and expanded to a pressure of 6 bar in the expansion vessel 10. At the top of the expansion vessel 10, 636 kg / hr of desorbed gases comprising substantially methane and ethane were extracted.

The absorber was removed at the bottom of the expansion vessel 10 and was conducted through the heat exchanger 11 in the desorption column 13 and heated thereto to 130.8 ° C by evaporator 15. The desorbed acid gases were cooled from 113.4 ° C to 40 ° C in the refrigerator 17. The 1875 kg / h aqueous phase formed in this process was separated from the acid gases in the phase separation unit 18. From the desorbent top condensate, 165 kg / h were removed and the rest was passed back into the desorption column.

The annual amine loss is 0.095 t; this is equivalent to 0.80% of the 12 t of the originally used amine.

Claims (1)

1. CLAIMS A process for separating acid gases from a fluid stream comprising water, wherein a) the fluid stream comprising water is contacted in an absorption zone with an absorbent comprising at least one amine, where a deacidified fluid stream and an absorbent charged with acid gas are obtained, b) the deacidified fluid stream is contacted with an aqueous washing liquid in a washing zone through which the washing liquid is conducted in a single passage without pumping it in circulation, in order to transfer entrained amine at least in part to the washing liquid, where a deacidified, deaminated fluid stream and a washing liquid charged with amine are obtained, c) the deacidified, deaminated fluid stream is cooled downstream of the washing zone, where a higher condensate Absorbent is condensed from the deamidated, deacidified fluid stream, d) the charged absorbent is passed to a desorption zone where the acid gases are released at least in part, where a regenerated absorbent and desorbed acid gases are obtained, e) the regenerated absorber returns to the absorption zone in order to form an absorbent circuit, f) the washing liquid loaded with amine and the upper absorbent condensate are introduced into the absorbent circuit, and g) the desorbed acid gases are conducted through an enrichment zone having a structured packing, a random packing and / or a plurality of trays and the acid gases that exit at the top of the enrichment zone are cooled, In order to condense a desorbent upper condensate from the acid gases that partly returns to the enrichment zone and partly leaves the process. The process according to claim 1, wherein the upper desorbent condensate comprises less than 500 ppm by weight of amines and amine decomposition products. The process according to claim 1 or 2, wherein the wash liquid comprises upper sorbent condensate, desorbent upper condensate and / or fresh water. The process according to any of the preceding claims, wherein the washing liquid loaded with amine is passed to the absorption zone. The process according to any of the preceding claims, wherein the deacidified, deaminated fluid stream is cooled in an indirect cooler. The process according to any of the preceding claims, wherein the deacidified fluid stream, The temperature is cooled to a temperature that is lower than the temperature of the fluid stream comprising water. 7. The process according to any of the preceding claims, wherein the enrichment zone has a structured packing, a random packing or a plurality of trays. 8. The process according to claim 7, wherein the structured packing or the random packing has a height of at least 1.5 meters. 9. The process according to claim 7, wherein the amount of the trays is at least 4. 10. The process according to any of the preceding claims, wherein the charged absorbent is regenerated in the desorption zone in at least one selected magnitude of expansion, distillation with an inert gas and heating. The process according to claim 10, wherein the absorbent charged with acid gases is preheated by indirect heat exchange with the regenerated absorbent before entering the desorption zone. 12. The process according to any of the preceding claims, wherein the charged absorbent is expanded in an expansion vessel, wherein a gas phase and an expanded absorbent are obtained and the expanded absorbent is passed to the desorption zone. 13. The process according to claim 13, wherein at least a part of the upper absorbent condensate is introduced into the expansion vessel. 14. The process according to any of the preceding claims, wherein the fluid stream comprising water has a water content that is at least 20% of the water saturation concentration. 15. The process according to any of the preceding claims, wherein the fluid stream comprising water is introduced into the absorption zone at a pressure of 50 to 70 bar. 16. The process according to any of the preceding claims, wherein the fluid stream comprising water has a partial pressure of acid gas of less than 2.5 bar. 17. The process according to any of the preceding claims, wherein the fluid stream comprising water is selected from a) natural gas, b) synthesis gas, c) exhaust gases from various refinery processes, d) combustion gases, or e) gas obtained from a Claus process. SUMMARY A process for separating acid gases from a fluid stream comprising water is described, wherein a) the fluid stream comprising water is contacted in an absorption zone with an absorbent comprising at least one amine, wherein a stream of deacidified fluid and an absorbent charged with acid gas is obtained, b) the deacidified fluid stream is contacted in a washing zone with an aqueous washing liquid, in order to transfer amine entrained at least in part to the liquid washing, where a stream of deacidified, dewatered fluid and an amine-laden washing liquid is obtained, c) the deacidified, deaminated fluid stream is cooled downstream of the wash zone, where an upper absorbent condensate condenses of the deamidated, deacidified fluid stream, d) the charged absorbent is passed to a desorption zone where the acid gases are released at least in part, where the they have a regenerated absorbent and desorbed acid gases, e) the regenerated absorbent returns to the absorption zone to form an absorbent circuit, f) the washing liquid loaded with amine and the upper absorbent condensate are introduced into the absorbent circuit and g) the acid gases desorbed are conducted through an enrichment zone and the acid gases that exit in the upper part of the enrichment zone are cooled, in order to condense of the acid gases a desorbent upper condensate that partly returns to the zone of enrichment and part of the process. The process allows an efficient retention of amines of the fluid streams treated with maintenance of the hydrologic equilibrium of the acid gas removal plant.